Biomedical subjects

A Peinado

Publications and source records attributed to A Peinado.

11 recordsLinked to original sources

PubMed1993

Extensive dye coupling between rat neocortical neurons during the period of circuit formation.

A low molecular weight intracellular tracer, Neurobiotin, was injected into single neurons in living slices of rat neocortex made at postnatal days 5-18. Between days 5 and 12, 66% of single-neuron injections labeled clusters of up to 80 neurons surrounding the injected cell. Coupling between neurons occurred primarily through dendrites. Injections done in the presence of halothane, a gap junction blocker, abolished the spread of tracer to surrounding neurons, implying that gap junctions mediate coupling. Injections done after day 16 resulted in little or no dye coupling. We conclude that transient local coupling via gap junctions in developing cortex may provide a pathway for communicating intercellular signals, including subthreshold electrical activity, and thereby enable temporal coordination of local neuronal ensembles during circuit formation.

Aging↗

PubMed1992

Neuronal domains in developing neocortex.

The mammalian neocortex consists of a mosaic of columnar units whose development is poorly understood. Optical recordings of brain slices labeled with the fluorescent calcium indicator fura-2 revealed that the neonatal rat cortex was partitioned into distinct domains of spontaneously coactive neurons. In tangential slices, these domains were 50 to 120 micrometers in diameter; in coronal slices they spanned several cortical layers and resembled columns found in the adult cortex. In developing somatosensory cortex, domains were smaller than, and distinct from, the barrels, which represent sensory input from a single vibrissa. The neurons within each domain were coupled by gap junctions. Thus, nonsynaptic communication during cortical development defines discrete multicellular patterns that could presage adult functional architecture.

Action Potentials↗

PubMed1991

Normally unused positional cues guide ectopic afferents in the leech CNS.

Central projections from peripheral sensory neurons segregate into distinct, ventrally positioned longitudinal tracts within the segmental ganglia of the leech Hirudo medicinalis. As documented here, there is an additional tract in the neuropils of the fifth and sixth body ganglia, located at the lateral margin and formed by afferent axons (the "sex afferents") originating from sensory neurons located in the male and female genitalia. Ablation of the genitalia results in the complete absence of this additional tract. We asked (1) whether segmental differences exist in the distribution of pathway cues available to the sex afferents, and (2) whether central pathway selection by these axons is specific. We transplanted the primordia of the male genitalia to several ectopic positions posterior to the sixth body segment and labeled the ectopic sex afferents in order to examine their paths in the CNS. In about 50% of the experimental animals, afferent axons originating in the transplanted tissue segregated into a distinct lateral fiber bundle within the neuropil of a nearby ganglion, in a position corresponding to their normal one in the sex ganglia. The sex afferents therefore find their normal pathways even in the ganglia of inappropriate segments, although these pathways are not used by any other afferents in these ganglia. We propose, therefore, that the positional cues employed by afferent axons to select appropriate pathways in the ganglionic neuropil are expressed in all segments of the leech CNS, regardless of whether such cues are normally used by afferent axons in each segment.

Afferent Pathways↗

PubMed1990

Segregation of afferent projections in the central nervous system of the leech Hirudo medicinalis.

Sensory axons originating in peripheral tissues converge onto each segmental ganglion in the central nervous system (CNS) of the leech, where they segregate into well-defined regions of the synaptic neuropil. Here we report on several aspects of the molecular and anatomical organizations of these afferent projections that bear upon the hypothesis that surface markers are involved in organizing these axons as they grow into the CNS. First, we show that the distribution of some surface markers in the adult is restricted to axons of peripheral origin and is not present on the neighboring axons of central neurons. Second, we demonstrate that the number of afferents increases postembryonically as the leech increases in size, suggesting that at least some of the cues employed by afferent axons to grow to appropriate central targets must be present throughout the life of the animal. We then show, using anterograde axonal tracing and immunohistochemistry, that there is both convergence and divergence of afferent axons into highly specific regions of the neuropil. Lastly, we examine the distribution of surface markers present on different subsets of afferents and show that axons having one type of marker segregate from those having the second type. Our results, considered together with previous observations in this system, provide new clues about the organization of afferent projections in the nervous system of the leech. They also suggest how a relatively small number of molecular markers might mediate fiber-fiber interactions to organize afferent axons as they grow into the CNS.

Afferent Pathways↗

PubMed1987

Regeneration of afferent axons into discrete tracts within peripheral nerves in the leech.

We have analyzed the pathway followed by regenerating afferent axons in peripheral nerves of the leech Hirudo medicinalis by anterograde labeling with horseradish peroxidase. We show that axons are able to reestablish appropriate pathways following a lesion (crush) which greatly disrupts the organization of the nerves. Our results are consistent with a pathway selection mechanism involving axon surface markers which are retained on the distal stumps of crushed axons.

Animals↗

PubMed1987

A group of related surface glycoproteins distinguish sets and subsets of sensory afferents in the leech nervous system.

The distribution of 4 surface glycoproteins on axons of peripheral neurons was studied in the leech Hirudo medicinalis through monoclonal antibodies. All 4 glycoproteins have a similar molecular weight of 130 kDa. Immunohistochemical localization of these glycoproteins on tissue sections of nerves and neuropil reveals tracts of afferent axons organized as nested sets. Their distribution suggests a possible role for these molecules in mediating axon fasciculation.

Animals↗

PubMed1987

Cell death during gangliogenesis in the leech: bipolar cells appear and then degenerate in all ganglia.

The bipolar cells can be recognized very early during gangliogenesis in the leech central nervous system by their expression of antigens that are recognized by the monoclonal antibody Laz1-1. They are the first cells to express these antigens, which are later shared with a distinct set of other cells in the leech nervous system. Their processes extend several segments rostrally and caudally along the forming interganglionic connective nerves; they are first found in anterior segments and gradually appear in more posterior ones over the course of 2-3 d. At about the time bipolar cells appear in the neuromeres of the tail ganglion, those in the most anterior segmental ganglia begin to degenerate. Degeneration proceeds caudally over the next 3 d, until all bipolar cells have disappeared. Bipolar cells are, thus, members of that class of cells that exists for only a short period in neurogenesis and then presumably disappears once its functions are no longer required. These cells' morphology and appearance at the earliest stages in the formation of the interganglionic connective nerves are suggestive of a role in the establishment of these longitudinal pathways in the leech CNS.

Animals↗

PubMed1986

Segmental differentiation in the leech nervous system: specific phenotypic changes associated with ectopic targets.

The issue of whether interactions between central neurons and the targets they innervate are involved in establishing segment-specific phenotypic differences in the central nervous system was evaluated by studying the effect of naturally occurring ectopic targets on individual identified neurons of the leech Hirudo medicinalis. The specimens studied were found to have additional sex organs located in segments adjacent to those containing the normal structures. We report our observations on neuronal morphology, the presence or absence of specific neurons, and total ganglionic cell number and discuss some of the possible ways in which the observed changes might have arisen.

Animals↗

PubMed1982

Determinations of gray cell coefficient in the dorsal lateral geniculate nucleus of the mouse.

This study is an analysis of the gray cell coefficient carried out in different regions of the dorsal lateral geniculate Nucleus (dLGN) of the mouse. We have analysed the contribution three different sized neuron types to the coefficient. Only about 6% of the total volume of the dLGN is occupied by nerve cell bodies, and the neurons that account for most of this 6% are medium sized (the largest diameter being between 8 and 11 microns.) The smallest neurons are mainly located in the more peripheral region of the nucleus.

Animals↗

PubMed1979

Distal radial epiphyseal displacement after impaired distal ulnar growth.

Impairment of growth of the distal end of the ulna was produced in rabbits by excision of the distal epiphyseal plate. This caused a sequence of changes in the distal radial epiphysis consisting of combined increased chondrogenesis and decreased osteogenesis of the radial two-thirds of the distal epiphysis, and decreased chondrogenesis and increased osteogenesis on the ulnar side. At six to nine days postoperatively, cracks appeared concomitant with tilting of the plate and epiphysis, in the epiphyseal plate or at its metaphyseal junction. An incomplete radial epiphyseal separation occurred, a step-like deformity developed in the metaphysis, and an ulnar deviation developed.

Animals↗

PubMedDate not supplied

Gap junctional communication and the development of local circuits in neocortex.

In the neocortex, as well as in many other brain regions, neurons responding to similar stimulus features are usually found close to one another. Here we examine the possible role of gap junctional communication in forming and defining these local neuronal groupings, examples of which may be the columns found in the neocortex of virtually all mammalian species. We have approached this question experimentally in cortical brain slices using calcium imaging to visualize multicellular activity patterns, and tracer injections to identify the anatomical pattern of gap junction coupling in the developing neocortex. Our results suggest that dendrodendritic gap junctional communication may be involved in the formation of local connectivity, most likely by synchronizing electrical or biochemical activity among neighboring neurons.

Animals↗